Electrostatic image liquid deformation development



United States Patent 3,196,009 ELECTROSTATIC IMAGE LIQUID DEFORMA- TION DEVELGPMENT Robert W. Gundlach, Victor, and George R. Mott and William D. Hope, Rochester, N.Y., assignors to Xerox Corporation, Rochester, N.Y., a corporation of New York Filed May 8, 1962, er. No. 193,246 5 Claims. (Cl. 96-1) This invention relates to electrophotographic image reproduction and in particular, to development by liquid deformation.

The more conventional electrophotographic reproduction processes, better known as xerographic processes, comp-rise the formation of a latent electrostatic image on a photoconductive insulating layer by electrostatically charging the layer and then exposing it to an image pattern of light and shadow. The electrostatic charge dissipates or leaks off the layer in proportion to the amount of illumination leaving a latent image which is then conventionally developed by contacting it with pigmented particles or toner which hear an electrostatic charge of opposite polarity to that of the latent image. While there have been many modifications to this basic process, it is only recently that attempts have been made to develop latent electrostatic images not with particulate developer material but by deforming a compliant layer in accordance with electrostatic forces. In this area of deformation imaging, one particular advantage lies in the erasability of such images. Thus, when a compliant layer is deformed in an image configuration by electrostatic forces, removal of the electrostatic forces may result in a loss or erasure of the image. For example, if a thermoplastic layer is positioned in the influence of a latent electrostatic image and heated to compliancy, it will deform in accordance with the image. Cooling will then freeze the image. Later, removal of the image from the presence of the electrostatic latent image and reheating will produce erasure so that the thermoplastic layer may be reused. Such thermoplastic materials as 'have been used in forming deformation images suffer from erasure lag and are inclined to change their physical and chemical characteristics so that after a period of continuous reuse, there is loss in reproduction quality.

In accordance with the present invention, it has been found that certain insulating liquids may be used in producing deformation images. With these liquids, it has been found possible to enhance the speed of image formation, to improve and speed up image erasure and to avoid deterioration in performance usually produced by continuous reuse of materials. Thus, it is an object of the present invention to define a method of deformation development.

It is a further object to define a method of forming images which may be replaced on the same media at high speed intervals.

It is a further objective to define a method of forming an image having high speed and facility of erasure.

Further objects and features of the invention will become apparent while reading the following description in connection with the drawings wherein:

FIGS. 1-4 are diagrammatic illustrations of the basic flow steps in the process of the present invention;

FIG. 5 is a cross-section of a xerographic plate carrying a deformation image in accordance with the present invention;

FIG. 6 is a diagrammatic illustration of image erasure in accordance with the present invention.

In the present invention, an image reproduction is obtained on the surface of a layer of liquid. A liquid layer is formed and then subjected to electrostatic forces proportional to the variations in the image so as to form deformations in the liquid surface corresponding to the image pattern. Thus, FIG, 1 is the first step in a basic embodiment for obtaining a liquid layer. Illustrated in FIG. 1 is a xerographic plate 10 comprising conductive backing 1 and photoconductive insulating layer 12. The conductive backing material can be brass, aluminum or other opaque metallic material or for certain applications, a transparent material that is conductive or has a conductive layer such as glass with an evaporated coating of tin oxide. The photoconductive insulating material can be vitreous selenium or zinc oxide dispersed in a binder material or any of the other photoconductive insulating compositons known in the art. A xerographic plate is shown positioned on electrically grounded support 13. Over the surface of photoco-nductive insulating layer 12, liquid layer 14 is formed by pouring a small amount of insulating liquid 15 from a container 16. This liquid desirably has certain characteristics. It preferably is highly resistant to electrical current so that a thin layer exhibits high lateral electrical insulation. Thus, it should have a surface resistivity of at least 10 ohms per square centimeter. While lower resistivities in the liquid could still sustain images, such images are highly fugitive and are shortly dissipated apparently due to lateral conductivity in the liquid. A further desirable characteristic is low volatility. Volatile materials would be used up at an excessive rate by evaporation unless the additional complexity of a gas seal is added to the equipment. Exemplary liquids are petro leum, low melting point parafiin, some vegetable oils such as olive oil, beeswax, and a number of petroleum products or distillates such as, for example, in one preferred embodiment, Stoddard solvent. In the case of normally solid materials such as paraflin or beeswax, it is necessary to apply sufficient heat to render them liq uid. While a large number of normally solid materials can readily be used by adding a solvent, this has not generally been found desirable because of the usually high volatility of the appropriate solvents.

A sufiicient quantity of the insulating liquid must be applied to the plate surface to allow for the depth of the relief image to be obtained. Usable images have a minimum practical depth requirement of about of 21 micron and a preferable relief depth is between .5 and 1 micron. A usable range of liquid layer thickness extends from about micron to 20 microns and is preferably between 1 and 10 microns. Thicker layers, it has been found, present flow problems and result in reduced resolution.

The liquid is then spread out over the xerographic plate by some convenient means such as by wiping or, as illustrated in FIG. 2, by running a roller 17 over the surface. Absolute uniformity is not essential since the liquid, itself, will tend to prevent any abrupt changes in layer thickness and variations in layer thickness that are gradual over a wide area do not significantly affect the image as it is reproduced. A liquid can also be applied by merely flowing it over the entire surface or by immersion and in any case, the thickness of the liquid layer thus produced will be determined largely by the viscosity of the liquid. Since the viscosity of many of the different liquids usable in this invention, as are described above, can vary over a Wide range, a liquid having a viscosity that will produce the desired layer thickness can be readily obtained. In some instances, it may be found desirable to vary viscosity by varying temperature. Many of the petroleum products having the desired characteristics for the present invention readily vary in viscosity with temperature.

After application of the liquid layer, an electrostatic charge is then applied over the liquid layer to sensitize c; the xerographic plate. FIG. 3 illustrates corona charging of the liquid layer. As illustrated in FIG. 3, a corona discharge device it; is connected to a high voltage source 20, the other side of which is connected in common with conductive support 13 which is conductively connected EULA A LlLllUl CL to the backing if of the xerographic plate. positive or negative charge maybe applied, but depending on the photoconductive insulator used, it may be preferable to use one or the other for optimum results. Thus, if the photoconductive insulator material is vitreous selenium, it is preferable to use a positive charge and, if the photoconductive insulator is zinc oxide in a binder, a negative charge is preferable. The layer may be charged to between 50 and 1300 volts depending somewhat on the characteristics of the liquid and the characteristics of the photoconductor and preferably is charged to a level of between 125 and 800 volts. Depending on the dielectric strength and thickness of the materials used, dielectric breakdown may occur at higher voltages while lower voltages tend to limit contrast.

During charging, exposing and visualizing, the liquid coated xerographic plate must be kept away from ambient lighting. In FIG. 4, the exposure step is illustrated in which xerographic plate it) is exposed to a pattern of light and shadow as from projector Ell. This pattern of light and shadow can be, for example, a light image of any physical object or scene as focused by'an DPlILdL system through liquid layer M and onto photoconductive insulating layer 12. Where illumination strikes photoconductive insulating layer 12, it becomes conductive. This selective conductivity in layer 12 produces an electrostatic latent image.

While FIG. 4 illustrates projection of the light image through insulating liquid layer 14, if the conductive backing of the xerographicplate is a transparent conductive layer, the light image may be focused on the photoconductive insulating layer by projection through such transparent backing layer. In the case of exposure through a transparent conductive plate backing it is sometimes convenient to use an opaque insulating liquid for the deformable layer. Use of an opaque liquid blocks one surface of the xerographic plate from extraneous light simplifying exposure and permitting ordinary illumination of the deformation image without dissipating the latent electrostatic image. In all instances a latent electrostatic image is formed in the xerographic plate.

FIG. 5 illustrates the deformation of a liquid layer in reaction to the latent electrostatic image as produced by the step of FIG. 4. Since the liquid layer 12 is highly compliant, the non-uniformity of the electrostatic forces causes a deformation of the surface of the liquid along the image gradients so that a deformation image is produced that corresponds to the original light image. It should be clearly understood that deformation as taught by the present invention can only occur along lines of substantial non-uniformity such as exists in a line image or at the edges of a solid area image. Thus, by image gradients it is intended to mean, here and in the claims, a substantial image edge rather than a continuous grad ual transition from light to dark. Thus, the gradient in the original image must be adequate to produce a voltage step on the xerographie plate during exposure.

The image thus formed may be utilized in various ways such as by reflecting a beam of light off it so that by way of example the light is specularly reflected in the uniform areas while it is refracted and dirfused in the deformed areas. The particular portions of the deformities which refract and diffuse is dependent on the angle of incidence of the light and may be varied as desired. It is of particular advantage in some utilizations that the image can be viewed directly during formation or while a projection from it is used to produce hard copy or for transmission via facsimile devices or the like. Where the backing of the xerographic plate is transparent, it is also possible to project some forms of light through the n. It- 1. M... n'- LLl'ctl, 1L uecomes uniformly cend cting will erase the image. To avoid this, one method is to use light that is wholly of a longer wave length than 600 millimicrons. In particular, vitreous selenium in the form it is conventionally used on xerographic plates is sensitive substantially only to light wave lengths below 600 millimicrons and so will not become conductive when illuminated by light totally above that wave length. Of particular use in xeroradiography, the liquid deformation image may be formed by X-ray exposure on a plate insensitive to visible light. Such a plate is described by way of example, in US. Patent 2,804,396 to Ullrich, Jr. After the X-ray image is formed, viewing in visible light will not erase the image. Also for X-ray use an opaque insulating liquid such as Stoddard solvent dyed with nigrosine may be used and will protect the xerographic plate from visible radiation but permit exposure and erasure by X-rays through the insulating liquid or through an opaque conductive backing. It is also possible to illuminate the liquid deformation image by a high intensity flash such as can be produced by a strobotron or photofias'n source producing high intens y light a period of of a second or less. As is evident, this latter means of illuminating the deformation image would require a utilization capable of reading the image at an extremely high rate of speed such as is possible with, for example, photography or xerography. In a still fur ther Way of utilizing the deformation image and more particularly where the liquid layer is a layer of low melting point paraffin, for example, the image may be frozen by cooling and hardening. Using paraliin, especially a low melting point paraffin, the layer 14 may be kept in a hard or frozen form until actual use and may then be liquified by the application of a small amount of heat. The liquid thus produced is considerably more compliant than the softened state readily achieved with the usual thermoplastic. After the deformation image has been formed, the paraffin may again be hardened and may be illuminated in such a way as to show up the image to the best advantage without loss due to dissipation of the electrostatic field forces.

The deformation image in this case can be formed simultaneously with exposure or subsequent thereto. If the material is soft or liquid during exposure it will deform simultaneously. On the other hand the material may be left solid during the exposure and as long as the latent electrostatic image is maintained as by protection from light, the deformable layer will deform anytime it is momentarily softened. Uniform illumination of the paraffin or other liquid or liquified layer by normal ambient lighting or light source 26 as illustrated by FIG. 6 will cause the deformations to immediately disappear and the layer will again be ready for use.

Whether the liquid layer is a liquid that always remains a liquid or whether it is parafiin which is intentionally kept in a liquid state, illumination of the xerographic plate W h the deformed liqui' layer over it by a light source 26 to which the plate is sensitive will cause rapid extinction of the latent image and the deformation image.

While the present invention has been described as carried out in specific embodiments thereof, there is no desire to be limited thereby, but it is intended to cover the invention broadly within the spirit and scope of the up pended claims.

What is claimed is:

ll. A method of electrophotographic image reproduction comprising the steps of:

(a) applying a uniform electrostatic charge to the surface of a charge deformable, electrically insulating liquid film overlying the photoconductive surface of a Xerographic plate; and,

(b) exposing said plate for a controlled time period to a pattern of light and shadow to be reproduced until said film in a liquid state is deformed in response to electrostatic charges at the image gradients conforming to said pattern.

2. A method of electrophotographic image reproduction, comprising the steps of:

(a) applying a uniform electrostatic charge to the surface of a charge deformable, electrically insulating liquid film overlying the photoconductive surface of a xerographic plate;

(b) exposing said plate for a controlled time period to a pattern of light and shadow to be reproduced until said film in a liquid state is deformed in response to electrostatic charges at the image gradients conforming to said pattern; and,

(c) uniformly illuminating said plate to dissipate said electrostatic charges whereby said liquid film is renewed for subsequent image deformation.

3. A method of electrophotographic image reproduction comprising the steps of:

(a) applying an electrically insulating liquid film to the photoconductive surface of a Xerographic plate comprising a layer of vitreous selenium on a transparent conductive backing,

(b) electrostatically charging and non-adjacent surface of said liquid film, and

(c) projecting a light and shadow image pattern through the transparent plate backing for a controlled time period until electrical charges migrate through the viterous selenium layer to the interface of said film whereby said film in a liquid state is deformed into a relief image corresponding to the image gradients of said pattern.

4. A method of electrophotographic image reproduction, comprising the steps of:

(a) coating a photoconductive surface of a Xerographic plate with a liquid paraffin layer between .5 and 10 microns thick,

(b) applying an electrostatic charge of at least 50 volts to the surface of said liquid parafiin,

(c) illuminating said photoconductive surface with a light pattern of the image to be reproduced for a controlled time period until causing charge fluctuations which deform said liquid parafiin in a relief reproduction corresponding to the gradients of said image, and

(d) cooling said liquid parafiin to its solidification temperature so that said reproduction may be retained in the presence of normal ambient light.

5. A recycling method of electrophotographic image reproduction comprising the steps of:

(a) coating the photoconductive surface of a Xero- 6 graphic plate with a transparent electrically insulating liquid film,

(b) applying an electrostatic charge to said film,

(c) exposing said plate to a pattern of light and shadow to be reproduced for a controlled time period until a latent electrostatic image is formed at the interface of said photoconductive surface and said film causing deformation of said film while in its liquid state in a reproduction of the image gradients of said pattern,

(d) utilizing said deformed image,

(e) uniformly illuminating said plate until said electrostatic latent image is dissipated to restore said film to uniformity, and

(f) repeating said steps of applying an electrostatic charge, exposing said plate to a pattern and uniformly illuminating said plate a plurality of times whereby a plurality of deformation images are sequentially produced in said film and are each successively erased from said film.

References Cited by the Examiner UNITED STATES PATENTS 2,008,746 7 35 Collins 9686 2,896,507 7/59 Mast et al.

2,901,348 8/59 Dessauer et al.

2,943,147 6/60 Glenn.

2,946,682 7/60 Lauriello 96-1 2,956,874 10/60 Giaimo 96-1 2,985,866 5/61 Norton 340-173 3,008,066 11/61 Newberry.

3,055,006 9/62 Dreyfoos et al. 961 3,063,872 11/62 Boldebuck 117-211 3,084,061 4/63 Hall 96-1 3,095,324 6/63 Cusano et a1 117215 3,108,893 10/63 Oliphant 11793.4

OTHER REFERENCES Selenyi, Photography on Selenium, Nature, vol. 161, page 522, April 3, 1948, column 1.

Cross, Deformation Image Processing, IBM Technical Disclosure Bulletin, vol. 4, No. 7, Dec. 1961, pages 35-6.

G.E. (I) Belgian Pat. 592,152 June 22, 1960. Abstract in: Recueil des Brevets dInvention (1960) June 30, 1961, vol. 6, page 1267.

GE. (11) Belgian Pat. 598,591 Dec. 28, 1960. Abstract in: Recueil des Brevets dInvention (1960) Sept. 2, 1962, vol. 12, page 2573.

Forster; J. Chem. Phys. 37, 10218 (1962).

Esso; Chem. & Eng. News, vol. 41, No. 23, page (book cover) June 10, 1963.

NORMAN G. TORCHIN, Primary Examiner. 

1. A METHOD OF ELECTROPHOTOGRAPHIC IMAGE REPRODUCTION COMPRISING THE STEPS OF: (A) APPLYING A UNIFORM ELECTROSTATIC CHARGE TO THE SURFACE OF A CHARGE DEFORMABLE, ELECTRICALLY INSULATING LIQUID FILM OVERLYING THE PHOTOCONDUCTIVE SURFACE OF A XEROGRAPHIC PLATE; AND (B) EXPOSING SAID PLATE FOR A CONTROLLED TIME PERIOD TO A PATTERN OF LIGHT AND SHADOW TO BE REPORDUCED UNTIL SAID FILM IN A LIQUID STATE IS DEFORMED IN RESPONSE TOK ELECTROSTATIC CHARGES AT THE IMAGE GADIENTS CONFORMING TO SAID PATTERN. 